The present invention relates to the fabrication of supported polycrystalline diamond or cubic boron nitride (CBN) compacts and especially to the preparation of such compacts utilizing thermally-stable polycrystalline diamond and CBN compacts.
Well known in the super abrasive art are compacts of polycrystalline abrasive particles typified by polycrystalline diamond and polycrystalline CBN compacts. Such compacts are represented by U.S. Pat. Nos. 3,745,623 and 3,608,818 with respect to polycrystalline diamond compacts and U.S. Pat. Nos. 3,767,371 and 3,743,489 with respect to polycrystalline CBN compacts. A supported polycrystalline compact is a compact attached to a reinforcing or substrate material, such as cemented metal carbide. In one configuration referred to as a supported wire die compact, a core of polycrystalline diamond or CBN is jacketed by an annulus or support of, for example, cemented carbide or stainless steel.
While such polycrystalline compacts represent a significant contributioon to the art in many fields of use, thermal degradation at an elevated temperature, e.g. above about 700.degree. C., limited their usefulness, especially in metal matrix bond applications. Thermal stability of such polycrystalline compacts was improved with the advent of thermally-stable, porous self-bonded diamond and CBN compacts containing less than about 3% non-diamond phase, hereinafter termed "porous compacts". Compacts of this type are the subject of U.S. Pat. Nos. 4,224,380 and 4,288,248.
For purposes of the present invention, so-called "direct conversion" CBN compacts are deemed to be thermally-stable. Direct conversion CBN compacts are disclosed in U.S. Pat. No. 4,188,194 and are made from preferentially oriented pyrolytic hexagonal boron nitride in the substantial absence of catalytically active materials. For purposes of the present invention, "re-sintered" polycrystalline CBN compacts also are thermally-stable. Re-sintered polycrystalline CBN compacts are taught in U.S. Pat. No. 4,673,414 and are made by re-sintering catalyst-free boron-rich polycrystalline cubic boron nitride particles under appropriate high pressure/high temperature (HP/HT) conditions.
European patent publication No. 116,403 describes a thermally-stable diamond compact comprising a mass of diamond particles present in an amount of 80-90% by volume of the body and a second phase present in an amount of 10-20% by volume of the body, the mass of diamond particles containing substantially diamond-to-diamond bonding to form a coherent skeletal mass and the second phase containing nickel and silicon, the nickel being in the form of nickel and/or nickel silicide and the silicon being in the form of silicon, silicon carbides, and/or nickel silicide. British patent application No. 8508295 describes a thermally-stable diamond compact comprising a mass of diamond particles present in an amount of 80-90% by volume of the compact and a second phase present in an amount of 10-20% by volume of the compact, the mass of diamond particles containing substantially diamond-to-diamond bonding to form a coherent skeletal mass and the second phase consisting essentially of silicon, the silicon being in the form of silicon and/or silicon carbide.
Diamond, synthetic or natural, is very difficult to wet, making the attachment of diamond to a variety of substrates difficult. Since thermally-stable compacts, and especially porous compacts, essentially are composed only of diamond or CBN (i.e. are substantially metal-free), they are difficult to bond to cemented carbide supports, for example. Bonding thermally stable compacts to carbide supports utilizing brazing alloys has been proposed, for example, in British Pat. No. 2,163,144 and in commonly-assigned U.S. Ser. No. 07/158,575, filed Feb. 22, 1988. Commonly-assigned U.S. Ser. No. 06/818,850, filed Jan. 14, 1986, now U.S. Pat. No. 4,797,326, on the other hand, proposes to separately form a sintered polycrystalline diamond or CBN compact, and a plastically deformable support, such as a cemented metal carbide support. The pre-sintered compact and support are mated and subjected to elevated temperature and pressure conditions sufficient to plastically deform the support surface into attachment with the compact surface. The process is especially adapted to attaching thermally-stable compacts to cemented metal carbide supports and may make use of an interface binder disposed between the respective surfaces being mated. Such interface binder may be a catalyst/sintering aid for the polycrystalline thermally-stable compact subjected to the bonding process.